The present invention relates to a pneumatic tire provided with a block pattern comprising blocks formed by circumferential grooves and transverse grooves, in particular, to a pneumatic tire capable of reducing pattern noise.
In a tire comprising a block pattern provided with a plurality of blocks on a tread surface wherein circumferential grooves extend in the circumferential direction of the tire and transverse grooves extend in the intersectional direction with the circumferential grooves, there is a problem that a block end of first ground contacting side taps on a road surface at a time of ground contacting and makes an impact noise. And, a vibration at the time of the impact causes exciting the air in the circumferential groove and generates columnar resonance.
To solve the problem, soft rubber has been used for the blocks to reduce the impact at the time of the block end taps a road surface so as to reduce the impact noise. Unfortunately, when the block rubber is too soft, the block deforms highly at a time of ground contacting, and compression and opening of the transverse grooves make loud air-pumping noise. This may cause more pattern noise by contraries, and there is fear of generating uneven wear. The pattern noise is defined here as entire noise arising from the tread pattern and comprising the above-mentioned impact noise, columnar resonance, air-pumping noise and the like, for example. It is therefore difficult to reduce sufficiently the pattern noise because rubber tenderization has its limit.
It view of such circumstances, to reduce the impact noise, Japanese Laid-open Patent Publication No. 2000-309207 discloses a tire comprising a block (a) provided with a large number of concave-or-convex non-flat portions (b) on a radially outer edge (ae) where a block wall surface (as) facing to a transverse groove and a tread surface (ts) meet. According to the Japanese Patent Publication No. 2000-309207, the above-mentioned non-flat portion (b) is dimple-like and flute-like. Disadvantageously, although having an effect on the reduction of the impact noise, the block has not been expected to have an effect on the reduction of the columnar resonance in the circumferential grooves.
Therefore, it's an object of the present invention to provide a pneumatic tire capable of removing pattern noise by reducing impact noise and columnar resonance while inhibiting air-pumping noise.